1. Field of Invention
This invention relates to improvements in mass data storage devices, and, more particularly, to improvements in circuits used to write user and servo data to data storage media, such as spinning magnetic disks, or the like, with a thin film data transducer, or head in mass data storage devices.
2. Relevant Background
Mass data storage devices of the type to which the invention pertains include hard disk drives that have one or more spinning magnetic disks or platters onto which data is recorded for storage and subsequent retrieval. Hard disk drives may be used in many applications, including personal computers, set top boxes, video and television applications, audio applications, or some mix thereof. Applications for hard disk drives are still being discovered.
Typically in a hard disk drive, a stack of rotating storage disks is provided. The disks are generally formed of a suitable substrate material, such as metal or glass, onto which a thin film magnetic storage medium has been vacuum sputter deposited. The disks are generally secured to a disk spindle that rotates the disk.
Servo synchronization data is imprinted onto the disks, typically by a servo writer during the manufacturing process of the mass data storage device in which the disks are included, by altering the magnetic domains on the disk in each sector of each track as it is being defined on the disks. Such servo imprints are used for identifying individual tracks, sectors, data beginning and ending locations, head alignment along the track, and so forth. The servo sectors are written by the disk drive manufacturer by a device known as a track writer, and are generally not re-written. The process of writing the servo sectors is known as hard formatting, as opposed to soft formatting, which is performed by the end user for different purposes.
Read/write transducers, or heads, are a part of the mass data storage device, and are carried by pivotally mounted arms extending over the surface of the disks to move the heads radially inwardly and outwardly over selected radial distances of the disks. The radial position of the write head arm is controlled in a known manner by a “voice coil” that receives positioning signals from a voice coil driver circuit.
As the heads fly over the disks along the paths of the track with which they are currently aligned, electrical currents are passed through the heads at strategic times, so that the heads will produce magnetic flux signals that are recorded onto or in the magnetic media of the spinning disk.
So-called magneto-resistive (MR) heads are becoming increasingly popular, and may be used in environments having very high disk drive densities with low power requirements. Despite the reduced power requirements of MR heads, one of the problems facing mass data storage device designers is that as write speeds demanded of the heads and their supporting electronics increase, so does the current required to develop the magnetic fluxes necessary to operate the writing functions of the heads. In the past, write drivers operated at 1 Gb/s during normal operation and <100 Mb/s during servo operation. Little care was taken to lower the power of the writer while running at lower servo data rates because the power was naturally reduced in those architectures at lower data rates. For example, the previous writers consumed about 2 watts at 1 Gb/s but consumed 0.5 watts at 100 Mb/s. Newer writers which are designed for 1.6 Gb/s have higher DC current (current that is used with no switching). Thus, newer writers consume 2 watts at 1.6 Gb/s and they consume 1.2 Watts at 100 Mb/s. Thus, there is a need for a smarter design which uses less power during servo operation.
As described above, servo write operations occurs only during drive manufacturing, and is a well controlled environment; however, even with careful selection of operating conditions, a 1.6 Gb/s design writer will consume 2 watts, and at data rates below 100 Mb/s will consume 1.2 watts. This results in the tolerable temperature of the integrated circuit on which the drive circuitry is constructed being exceeded, and needs excessively large power busses to not exceed electromigration rules.
What is needed therefore, is a write driver that can be controlled to achieve the needed servo and data write functions without exceeding the current and power limitations of the writer circuitry.